The objectives of this research are to elucidate the role of 8-hydroxy-7-demethyl-5-deazaflavin coenzymes and nickel-dependent enzymes in the biogenesis of natural gas from C02 and H2 by methanogenic bacteria. The deazaflavins are structural and functional hybrids between nicotinamide and flavin coenzymes and are used as low potential redox currencies. We will elucidate redox stereochemistry, modes of deazaflavin biosynthesis, enzymic nucleotidylation reactions and other roles as coenzymes in the action of DNA photolyase, involved in photomonomerization of thymine dimer lesions in DNA. Over the past five years four novel nickel-containing enzymes have been detected and purified from methanognic bacteria. We are studying two nickel-containing hydrogenases, nickel-linked methyl-S-coenzyme M reductase, and a nickel-dependent CO dehydrogenase as nickel hydrogenation biocatalyst, nickel desulfurization biocatalyst, and nickel carbonylation biocatalyst, respectively. We shall continue efforts to analyze the structure of the nickel active sites to identify ligands nickel oxidation states and geometries to understand catalytic function.